It is known to provide wavelength selective switching in optical networks using a network element called ROADM (Reconfigurable Optical Add/Drop multiplexer). ROADMs are currently the fundamental blocks to build optical meshed networks and are becoming widely deployed in the core and metro/core segments. The increase in IP traffic is pushing a reduction in network layers leading to the IP/DWDM paradigm where the photonic infrastructure is directly connected to the IP/router layer. Therefore ROADM nodes are becoming part of the IP/DWDM solution and are going to be deployed to provide photonic switching to the IP layer enabling efficient multilayer switching.
It has been proposed to auto-discover optical system topology using tone signals to trace wavelengths through the network, or using a low-level wavelength-tunable monitor signal to probe the system. These tend to add complexity to transmitter design or are limited to discovering topology of lines between nodes rather than connections internal to nodes. It is also known to have nodes configured to transmit and receive a topology wavelength both external to the node and to one or more components in the node, wherein the topology wavelength is dedicated to providing topology discovery. Again this adds hardware and so adds complexity and costs, which increase as the ROADMs have more internal connections. Current ROADMs can have a large number (called degree) of interconnected subsystems (9-degree ROADMs are widely deployed and 20-degree ROADMs are already available) and can have a variety of functionalities (for example directionless, colorless, etc). When nodes are installed or upgraded, they may have complex commissioning and configuration procedures where mistakes can lead to wrong network operations.